Contactless monitoring of the diameter-dependent conductivity of GaAs nanowires

Abstract

Contactless monitoring with photoelectron microspectroscopy of the surface potential along individual nanostructures, created by the X-ray nanoprobe, opens exciting possibilities to examine quantitatively size-and surface-chemistry-effects on the electrical transport of semiconductor nanowires (NWs). Implementing this novel approach-which combines surface chemical microanalysis with conductivity measurements-we explored the dependence of the electrical properties of undoped GaAs NWs on the NW width, temperature and surface chemistry. By following the evolution of the Ga 3d and As 3d core level spectra, we measured the positiondependent surface potential along the GaAs NWs as a function of NW diameter, decreasing from 120 to ~20 nm, and correlated the observed decrease of the conductivity with the monotonic reduction in the NW diameter from 120 to ~20 nm. Exposure of the GaAs NWs to oxygen ambient leads to a decrease in their conductivity by up to a factor of 10, attributed to the significant decrease in the carrier density associated with the formation of an oxide shell.

Band bending at the heterointerface of GaAs/InAs core/shell nanowires monitored by synchrotron X-ray photoelectron spectroscopy

“…This observation implies that the origin of this energy shift depends mainly on the shell thickness and is not affected by the charging effect (if any) as reported in Ref. 17.…”

“…[12][13][14][15] Furthermore, this method has been successfully applied for the investigation of the structure and chemical composition of surfaces and interfaces of semiconductors NWs, e.g., to study the composition and removal of surface oxides on InAs NWs 16 or to probe the size and oxidation dependence of the conductivity in GaAs NWs. 17 However, there is a lack of XPS studies on core/shell heterostructure NWs, so far. In this work, we report on high resolution XPS investigation of GaAs/InAs core/shell NWs by means of synchrotron radiation, to monitor the band bending effect at the heterointerface and changes in surface electronic states due to the removal of the native surface oxides after a cleaning process.…”

Strong Schottky barrier reduction at Au-catalyst/GaAs-nanowire interfaces by electric dipole formation and Fermi-level unpinning

“…This value is in good agreement with the experimental value of 30 A V À 1 cm À 2 deduced from our STM measurements. We therefore attribute the observed large ideality factor to surface depletion 23,25 due to NW surface oxidation 26,27 , an effect that we discussed above for NWs from series A. Mechanisms responsible for the low Schottky barrier. To elucidate the physics behind this surprisingly low Schottky barrier, we will discuss several mechanisms that could be responsible for this result.…”

“…In fact, to the best of our knowledge, this is the smallest Schottky barrier height ever reported for Au/GaAs interfaces. An important comment to this analysis is that the effective contact area A between the Au catalyst and GaAs NW most likely depends on the applied bias 23 V app owing to self-gating effects 24 in combination with a surface depletion 23,25 due to NW surface oxidation 26,27 . However, such effects will not affect the extracted barrier height, as evident from equation (1) as well as from the saturation of the barrier height observed in Fig.…”

“…Our experimental design ensured that the effect of TE dominates over TFE since kT4 4E 00 , where E 00 is a property of the semiconductor indicating how efficient tunnelling is in the semiconductor 3 . For the studied NWs, E 00 o7 meV (since the NW geometry increases the depletion region 11,26 ) while the measurements were done at room temperature (kT ¼ 26 meV). Furthermore, a theoretical value of the expected low-bias differential conductance for TE 11 given by dJ=dV ¼ ðqA Ã T 2 =kTÞexpð À qf S =kTÞ at 300 K with A* ¼ 7 A cm À 2 K À 2 and qf S ¼ 0.35 eV yields 32 A V À 1 cm À 2 .…”